The present invention relates to a high-pressure bulge-forming apparatus. More particularly this invention concerns such and apparatus for producing complexly shaped hollow articles from a normally tubular workpiece.
It is known to bulge-form a tubular workpiece with an apparatus that has a stationary base, a die fixed on the base and formed with a cavity having an inner surface and axially oppositely open ends. A tubular workpiece can be held in the cavity with ends of the workpiece exposed at the ends of the cavity. A pair of pistons can be fitted to the workpiece ends in the cavity. Respective actuators displace the pistons toward each other and against the ends of the workpiece in the cavity. A hydraulic liquid is fed at high pressure through one of the pistons to an interior of the workpiece in the cavity to deform the workpiece. In this manner, as described in xe2x80x9cWerkstatttechnik 79 (1989)xe2x80x9d (VDI-Fortschrittsberichte, vol 2, no 142, VDI-Verlag 1987) it is possible to deform the normally tubular workpiece into a complexly shaped finished article whose outer surface conforms exactly to the inner surface of the die and whose inner surface is very smooth.
Normally the die is made in two parts and the workpiece, of steel or copper, is a simple cylindrical tube laid in the die cavity. The inner ends of the pistons are constructed to seal tightly against the ends of the tube, and normally the pistons are advanced coaxially inward as the workpiece is deformed, since typically it shortens somewhat as it expands radially outwardly.
Each forming operation therefore requires that the two pistons move axially into and out of the ends of the die cavity while exerting considerable axial force against the workpiece on the inward stroke. As a result of the considerable wear, the service life of such pistons is regrettably short. Thus changing them for new ones not only entails a considerable expense for the new parts, but considerable down time for the equipment while the relatively massive and moderately complex parts are swapped out with fresh ones. Similarly when the die and/or workpiece shape change, the pistons must be changed to accommodate the new size and/or shape.
It is therefore an object of the present invention to provide an improved high-pressure bulge-forming apparatus.
Another object is the provision of such an improved high-pressure bulge-forming apparatus which overcomes the above-given disadvantages, that is which can be easily and inexpensively refitted when the pistons are worn or workpiece format changes.
A high-pressure bulge-forming apparatus has according to the invention a multipart die having a cavity adapted to receive a hollow workpiece and having ends oppositely open along an axis. Respective actuators aligned with the cavity ends have stems extending axially toward the cavity. Respective heads on the ends are engageable in the cavity with ends of the workpiece. One of the stems and the respective head is formed with a passage opening axially into the workpiece engaged by the respective head. Fasteners releasable secure the heads on the stems.
Thus when the heads become worn or workpiece format changes, the heads can be swapped out for new ones. Since the stems and heads are completely withdrawn from the die between work cycles, they are fully exposed and it is relatively easy to unfasten the heads and switch them for new ones.
Each head according to the invention comprises an end part with an inwardly tapered outer surface and a base part fixed to the respective stem and carrying the respective head. In addition each head has a normally annular mounting plate between the respective base part and end part. Each mounting plate forms a shoulder axially engageable with the respective end of the workpiece. Alternately each end plate forms a shoulder axially engageable with the respective end of the workpiece.
The end part and mounting plate in accordance with the invention are hardened. They may be made of a particularly wear-resistant material such as bronze or a bronze alloy, e.g. Gz-CuAlBzNi or AMPCO 25. Such materials will slide particularly smoothly into the workpiece to be deformed. In addition the base part is formed of such a highly wear-resistant material.